This invention relates to a method and apparatus to visualize an internal mammary artery (IMA), and more particularly, it relates to a method and apparatus to visualize and widen an internal mammary artery which has been used as a bypass graft without direct cannulation of the internal mammary artery.
Coronary bypass surgery involves shunting blood from the aorta to branches of the coronary arteries in order to increase blood flow beyond a local obstruction. The conduits used to divert or channel blood flow from the aorta are constructed from tissue taken from another part of a patient's body. The use of internal mammary artery (IMA) grafts for myocardial revascularization was introduced in 1969. (The term "graft" refers to the artery after bypass surgery as distinguished from "native vessel" or simply "IMA" which refers to the artery before the operation.) The recent resurgence in the advocacy of its use as the graft of choice is due to favorable long-term follow-up studies which demonstrate that this artery is resilient, adaptable, and durable.
Before and after bypass surgery, it is useful to examine the IMA and to repair it if necessary. Angiography is a desirable preoperative and follow-up procedure to bypass surgery because it enables a physician to visualize the integrity of the IMA using radiography after the injection of a radiopaque material into the vessel. Preoperative arteriography has also been advocated for assessing the utility of an IMA as a bypass graft. IMA arteriography allows comparison of the IMA caliber with the recipient coronary artery. See Singh, R., Cath. Card. Diag. 6:439-449 (1980). Reconstructive techniques are necessary to combat atherosclerosis, a natural, on-going process which results from a build-up of atherosclerotic and/or fibrocellular deposits within vessel walls. Balloon angioplasty, one such technique for treating stenosed vessels, may thus extend the useful life of a graft.
Unfortunately, the right and left internal mammary arteries are easily damaged using traditional angiography and angioplasty procedures. Guaranteed safe cannulation of the internal mammary artery during catheterization remains unrealized. Although dissection and occlusion of the IMA by the catheter tip is an uncommon consequence of catheterization, it is a serious complication. The mechanical sheer stress applied by the catheter to internal vascular walls may remove endothelium and expose subendothelial thrombogenic tissues. Consequently, platelets may adhere to these exposed surfaces and cause the release of platelet-derived growth factors resulting in possible smooth muscle proliferation and fibrous tissue deposition. See Pap, J., Cath. Card. Diag. 13:57-73. Even though native internal mammary arteries rarely develop atherosclerosis, surgical manipulation of the IMA during bypass surgery may lead to intimal damage and subsequent stenosis of these fragile vessels. The site of stenosis is usually the point where the IMA is anastomosed to a coronary artery. PCTA of the stenotic or occluded right and left IMA graft has been reported as a successful therapeutic modality for restoring normal flow to a grafted coronary artery without need to perform a repeat bypass operation. It involves placing a modified balloon catheter into the IMA via a vascular puncture in the femoral or brachial artery under local anesthesia. Inflation of the balloon within the narrowed section of the IMA widens the vessel lumen and restores normal blood flow. A guiding catheter (8-9 French) which is as large or larger than the ostium of the IMA, is placed so that its tip intubates the ostium of the IMA. Stabilization of the catheter is, in part, dependent upon this contact point. On the other hand, this intubation may cause mechanical stress and the aforementioned possible tissue damage.
Other methods of removing arterial obstructions involve purposeful selective intubation of a guiding catheter into the IMA to facilitate distal advancement of a balloon catheter, in particular, a dilatation catheter. Due to the angulated origin and smaller caliber of the IMA compared to the coronary arterial ostium, the IMA is probably more susceptible to dissection during selective arteriography. Reported cases of IMA dissection demonstrate the vulnerability of this artery to conventional selective catheterization techniques. (The term selective catheterization techniques encompasses selective arteriography and selective angioplasty. It refers to the standard practice of inserting a catheter into the subclavian artery and thence directly into the IMA.) In one case, selective catheterization caused ostial left IMA graft dissection resulting in a massive anteroseptal myocardial infarction. The dissection in that case was not recognized at the time of the catheterization. The recent resurgence of interest in using internal mammary arteries for coronary revascularization mandates more frequent IMA evaluations before and after contemplated coronary bypass surgery.
Certain anatomical features of the left and right internal mammary artery obviate simple selective catheterization and arteriography. A significant characteristic is the variable location of the junction of the internal mammary artery and the subclavian artery along the subclavian artery. In most cases, the junction of the IMA and the subclavian artery is on the inferior and slightly anterior surface of the subclavian artery, approximately 1-4 cm distal to the point where the subclavian artery originates. The standard method for catheterization of the left IMA from the femoral approach is the passage of a 0.035 J-tipped guide wire through a 7 or 8 French Right Judkins or preformed IMA catheter into the left subclavian artery. After the guide wire is successfully advanced past the presumed junction of the IMA and the subclavian artery, the catheter is then advanced over the guide wire to a distal position, usually near the origin of the axillary artery. (The axillary artery is a continuation of the subclavian artery.) The catheter is then withdrawn so that its acutely angled tip is dragged along an infero-anterior plane. Although occasional non-selective injections may identify the junction of the IMA and the subclavian artery, selective intubation usually requires careful catheter manipulation and withdrawals along different planes. This procedure may cause significant intimal damage and adds to the time required for arterial catheterization. Furthermore, once the ostium of the IMA is located, the difficulty associated with controlling the depth or alignment of the catheter tip within the IMA increases the risk of IMA trauma during contrast injection.
A special IMA catheter has been developed with acute primary and secondary 80 degree curves that can be used from the right brachial artery approach. See Singh, R., Cath. Card. Diag. 6:439 (1980). No guide wire is required. The catheter is advanced distally into the subclavian artery, and "some manipulation is necessary to engage the tip into the orifice [of the IMA]." Of 75 patients studied, this catheter was successful in selectively intubating the left IMA in 78% and non-selectively in another 16%. Citing "inherent technical problems" with the femoral approach, Dorros and Lewin proposed an ipsilateral brachial approach for placing a guiding catheter into the right and left IMA for angioplasty. See Dorros, G., and Lewin, R., Cath. Card. Diag. 12:341-46 (1986).
In a review of clinical and angiographic characteristics of IMA-coronary bypass grafts, 124 out of 217 patients were monitored with digital subtraction angiography (DSA) arteriography. See Rankin et al., J. Thorac. Card. Surg. 92:832846 (1986). DSA, a non-invasive form of arteriography which produces an image of inferior quality to selective angiography, was preferred over catheterization for many reasons, including technical catheterization difficulties and "improved visualization in patients with subclavian artery tortuosity or anomalous IMA origin."
A method of reliable subselective catheterization that does not involve direct cannulation but does allow highly specific access to the internal mammary artery for arteriography and angioplasty is needed in order to fully exploit this proven and widely used bypass graft.